P&W v Rolls Royce on 757
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P&W v Rolls Royce on 757
Which is the most efficient engine fitted to the 757: the Pratt & Whitney or the Rolls Royce? I always assumed it was the Rolls Royce engine but I read some data yesterday (admittedly published by P & W) that on a Frankfurt - New york sector you can carry an extra 55 pax or over 5 tonnes of freight more than a Rolls Royce engined aircraft. If the P & W engine is more efficient why have more customers chosen the Rolls Royce engine? Can anyone enlighten me?
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I understand, although I can't find the data to back this up, that the Rolls Royce engine is superior on just about every count. Except....it is considerably heavier than the P & W. Perhaps a tonne a side, I doubt that it is two and a half tonne a side to give creedence to the P & W claim of a five tonne payload increase.
The inference here is that the Rolls Royce engine burns less fuel even when hauling along it's own extra lard.
I think the P & W claim whilst perhaps true, is being very selective.
Based on my probably inaccurate hypotheses and fag packet calculations:
If you require an aircraft which flies sectors which require more than 30 tonnes of fuel (ball park 3000nm or more) Get P & Ws.
For anything else use Rolls Royce.
The inference here is that the Rolls Royce engine burns less fuel even when hauling along it's own extra lard.
I think the P & W claim whilst perhaps true, is being very selective.
Based on my probably inaccurate hypotheses and fag packet calculations:
If you require an aircraft which flies sectors which require more than 30 tonnes of fuel (ball park 3000nm or more) Get P & Ws.
For anything else use Rolls Royce.
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I think the P&W claim here is just plain wrong.
757-200 Operating Empty Mass:
with P&W Engines - 57,840kg
with RR Engines - 57,975kg
So each RR engine weighs 67.5 kg more than a P&W engine. Pretty irrelevant if you ask me.
And just to be sure, in case the claim refers to the 757-300:
OEM with P&W Engines - 64,460kg
OEM with RR Engines - 64,590kg
Even less of a weight difference....
757-200 Operating Empty Mass:
with P&W Engines - 57,840kg
with RR Engines - 57,975kg
So each RR engine weighs 67.5 kg more than a P&W engine. Pretty irrelevant if you ask me.
And just to be sure, in case the claim refers to the 757-300:
OEM with P&W Engines - 64,460kg
OEM with RR Engines - 64,590kg
Even less of a weight difference....
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The following engines are approved for the 757-200:
RR RB211-535-C-37: 36,720 lbs
RR RB211-535-E4-37: 39,610 lbs
RR RB211-535-E4-B-37: 42,560 lbs
P&W PW2037: 37,530 lbs
P&W PW2040: 40,900 lbs
To compare PW with RR you would need to know the correct engine model.
Comparing PW2040 with RR 535-E4-37 (almost same thrust) the PW would come out on top regarding fuel usage.
Ex.: GW 240.000 lbs, FL350, mach 0.8: The PW2040 uses approx. 220 lbs less (per engine) per hour.
RR RB211-535-C-37: 36,720 lbs
RR RB211-535-E4-37: 39,610 lbs
RR RB211-535-E4-B-37: 42,560 lbs
P&W PW2037: 37,530 lbs
P&W PW2040: 40,900 lbs
To compare PW with RR you would need to know the correct engine model.
Comparing PW2040 with RR 535-E4-37 (almost same thrust) the PW would come out on top regarding fuel usage.
Ex.: GW 240.000 lbs, FL350, mach 0.8: The PW2040 uses approx. 220 lbs less (per engine) per hour.
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If those figures are correct, it leaves us with with a bit of an enigma. Why do 80% of operators opt for an engine that is heavier, thirstier and I would guess more expensive on initial purchase.
Which RR engine is your comparison based on GS? The E4 model according to the RR website has a range of 600nm more than the C model.
Which RR engine is your comparison based on GS? The E4 model according to the RR website has a range of 600nm more than the C model.
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BH, that's a good question.
The P&W is a lighter engine, and does normally give a little bit longer range. However I understand that the RR is a quiet engine, and has historically demonstrated greater reliability in service. I think the reliability of the RB211-535 series has been the overriding factor in chosing the RR engines over the P&W. I also think that on this aircraft (757), RR seems to always be first with delivery of the next higher thrust class engine when it was requested by Boeing, which doesn't hurt sales. The RR (RB211-535C) was also the first engine to be certified on the 757 when it was first introduced by Boeing. The PW2000 was a late comer.
In other words, RR seems to have always been in the lead with engines for the 757.
The P&W is a lighter engine, and does normally give a little bit longer range. However I understand that the RR is a quiet engine, and has historically demonstrated greater reliability in service. I think the reliability of the RB211-535 series has been the overriding factor in chosing the RR engines over the P&W. I also think that on this aircraft (757), RR seems to always be first with delivery of the next higher thrust class engine when it was requested by Boeing, which doesn't hurt sales. The RR (RB211-535C) was also the first engine to be certified on the 757 when it was first introduced by Boeing. The PW2000 was a late comer.
In other words, RR seems to have always been in the lead with engines for the 757.
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Being somewhat vexed by this question I have done a bit of research. The reliability of the Rolls engine is very good, An Icelandair 757 with an RB211-535-E4 clocked up world record 40,531 hours on the wing recently.
However the RB211 is heavier and does burn slightly more fuel, (comparing like with like, 535-E4 with PW 2037), and the old beancounters are not going to take that unless there are other compelling reasons
The crunch may be in the take off performance. At 250,000lbs, sea level, standard day, the RR engined 757 requires 6800ft of runway. The PW2037 requires 8700ft.
(Assuming I have read the graphs corrrectly, by no means guaranteed, it's been a year or two since Perf A)
I suspect that on European routes, that field requirement is probably unacceptable. The climb performance is presumably similarly disadvantaged and would I suspect make the PW aircraft next to useless for a charter operator.
Info is Here
Anyone got any better ideas?
However the RB211 is heavier and does burn slightly more fuel, (comparing like with like, 535-E4 with PW 2037), and the old beancounters are not going to take that unless there are other compelling reasons
The crunch may be in the take off performance. At 250,000lbs, sea level, standard day, the RR engined 757 requires 6800ft of runway. The PW2037 requires 8700ft.
(Assuming I have read the graphs corrrectly, by no means guaranteed, it's been a year or two since Perf A)
I suspect that on European routes, that field requirement is probably unacceptable. The climb performance is presumably similarly disadvantaged and would I suspect make the PW aircraft next to useless for a charter operator.
Info is Here
Anyone got any better ideas?
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Bally:
I was comparing PW2040 with the RR E4-37. (both in the neighbourhood of 40.000 lbs thrust.)
If you do that, you will also see that they have more or less the same field performance.
The PW2037 would compare to the RR C model.
I was comparing PW2040 with the RR E4-37. (both in the neighbourhood of 40.000 lbs thrust.)
If you do that, you will also see that they have more or less the same field performance.
The PW2037 would compare to the RR C model.
